One type of image-reading device known in the art conveys an original sheet and reads an image from the original sheet as the sheet passes through the read region of an image-reading unit. This type of image-reading device determines whether the leading edge or the trailing edge of the original sheet has arrived at the read region and uses the determination results to set a read timing for the image-reading unit, the size of the original image included in the read image, and the like.
One example of this image-reading device disclosed in Japanese Patent Application Publication No. 2004-120425 includes an original-pressing plate disposed opposite the image-reading unit. On the original-pressing plate is depicted an identification image, such as a pattern with colors changing along a main scanning direction, a bar code, or a special design. The image-reading device determines that the leading edge or the trailing edge of the original sheet has arrived at the read region by determining whether the image data read by the image-reading unit is data for the identification image or other image data.